Brown meat: Set instant pot to sauté. Add oil to pot and add thighs skin-side down. Cook, in batches if needed, until golden and crisp. Flip and cook until browned on the other side. Remove chicken from pot.

Start sauce: Add onion and garlic to pot and cook until starting to soften, about 1 minute. Add chicken broth, lemon juice, herbs and seasoning. Stir, scraping the browned bits off the bottom of the pot.

Pressure cook: Place chicken thighs back in the instant pot. Secure lid and set the pressure valve to “sealing”. Choose “pressure cook” (or “manual”) and “high” for 12 minutes (for large thighs, about 2 thighs per pound; cook for 8 minutes if chicken thighs are small, about 4 thighs per pound). Naturally release pressure after cooking time is up (just switch off the instant pot and leave it alone until pressure is gone).

Finish sauce: Carefully remove thighs. Set the Instant Pot to sauté. Pour cornstarch slurry into pot, stir well and simmer until sauce has thickened. Stir in butter until melted, then serve sauce over chicken with lemon slices, if desired.